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i think a good challenge would be to take a character from an old 3D game that has a really low polygon count and remake it. like how the FF7 characters went from being people with cubes for hands to super detailed people
there haven't ben any dynamics challenges... at least not for a couple of years. or how about rigging and animation. (not that i would join in that one.)
Rigging very hard to judge and not many know dynamics (me included) - animation should be on the cards but I think a rig would have to be offered.
how is rigging and animation hard to judge? rigging alone perhaps, but you can have crap rigs and good rigs, and more complicated rigs with good skinning just like you can have crap models and such. All you need to do is make a playblast of an animation showing all the things the rig can do.
and how come you don't want to learn dynamics? well at least it sounds like you don't. A dynamics challenge would be exactly that... a challenge. .
Animation challenges have hardy had any participation. I think 2 or 3 people entered if I remember correctly, so animation challenges are not a good idea IMO, at least not here. Gamers challenges are like a dime a dozen now. There's nothing really unique about them anymore.